Copper containing igniter composition for a gas generant

ABSTRACT

An igniter composition for a gas generant and a related method of igniting a gas generant are provided in which, in addition to a boron fuel component and an oxidizer component, the igniter composition additionally includes a gas-forming source of a condensable metal effective for transferring heat to the gas generant.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to the ignition of a gasgenerant such as those used for the inflation of inflatable devices likeairbag cushions included in inflatable restraint systems for automobilepassengers. In particular, the invention relates to an ignitercomposition which, upon combustion, produces a quantity of gaseousproducts and a quantity of condensable copper metal effective to conductheat to and ignite a gas generant.

[0002] It is well know to protect a vehicle occupant using a cushion orbag, e.g., an “airbag cushion” that is inflated or expanded with a gaswhen a vehicle experiences sudden deceleration, such as in the event ofa collision. Such airbag restraint systems normally include: one or moreairbag cushions, housed in an uninflated and folded condition tominimize space requirements; one or more crash sensors mounted on or tothe frame or body of the vehicle to detect sudden deceleration of thevehicle; an activation system electronically triggered by the crashsensors; and an inflator device that produces or supplies a gas toinflate the airbag cushion. In the event of a sudden deceleration of thevehicle, the crash sensors trigger the activation system which in turntriggers the inflator device which begins to inflate the airbag cushionin a matter of milliseconds.

[0003] Many types of inflator devices have been disclosed in the art forinflating one or more inflatable restraint system airbag cushions.Inflator devices which form or produce inflation gas via the combustionof a gas generating material, e.g., a “gas generant”, are well known.For example, inflator devices that use the high temperature combustionproducts, including additional gas products, generated by the burning ofthe gas generant to supplement stored and pressurized gas to inflate oneor more airbag cushions are known. In other known inflator devices, thecombustion products generated by burning the gas generant may be thesole or substantially sole source for the inflation gas used to inflatethe airbag cushion.

[0004] A number of gas generant compositions are known that include acopper-containing fuel or oxidizer. Such fuels or oxidizers aretypically employed in gas generant compositions because they produce alower level of undesirable gas products and limited amounts of toxic orirritating particulate material. Furthermore, copper complex fuels oftenutilized in gas generant compositions may advantageously producefilterable solid slag that can be relatively easily removed from the gasstream. In some cases, a fuel such as boron is included in a smallquantity to enhance gas generation during combustion. Generally, thecopper complexes are present in such gas generant compositions in asignificant amount such as greater than about 30 composition weightpercent. Some copper complex-containing gas generant compositions aredisclosed in, for example, U.S. Pat. No. 5,635,668 issued to Barnes etal., and U.S. Pat. Nos. 6,077,372 and 6,143,102 issued to Mendenhall etal., the disclosures of which are hereby incorporated by reference.

[0005] Often such inflator devices also include an initiator, such as asquib, and an igniter composition to ignite the gas generant. Inpractice, upon receipt of an appropriate triggering signal from a crashor deceleration sensor, the initiator activates causing the rapidcombustion of the igniter composition, which in turn ignites the gasgenerant. The igniter composition may be incorporated into the igniterdevice in various forms such as a granular material in a separatecontainer within the inflator housing, may be present as a pressedsleeve surrounding the gas generant, or may be coated directly onto thegas generant granules or tablets.

[0006] Igniter compositions are generally formulated to be very hotburning materials that rapidly combust and readily ignite the gasgenerant. Unfortunately, such compositions can generate undesirabletoxic gas species such as carbon monoxide or nitric oxide. Therefore,the quantity of igniter composition present in the inflator device iskept as low as possible but in a quantity sufficient to provide thedesired ballistic response (e.g., low delay time and proper pressurerise rate for the correct timing between the accident and the provisionof safety via the inflated airbag cushion).

[0007] However, the ignition of a gas generant by an igniter compositionis a function of various factors including the heat output of theigniter composition, the gas output of the igniter composition, and thethermodynamic properties of the gas generant, for example. Thus, if theigniter composition is present in a relatively low quantity it must bothgenerate heat and effectively transfer heat to the gas generant toachieve the proper ballistic response. Heat conduction to the gasgenerant from the gas products produced by combustion of the ignitercomposition is governed by heat content and the flow rate of the gasproducts. The presence of condensable ignition products can also play animportant role in the ignition process by transferring heat byconduction to the gas generant. In considering the relative efficiencybetween the two mechanisms (heat transfer from gases or condensed phaseproducts) both are necessary to achieve rapid and efficient ignition ofthe gas generant.

[0008] Several igniter compositions have been formulated to includeboron as a significant ingredient because it generates a significantquantity of heat. Often, however, the boron fuel is present in asignificant amount such as greater than about 10 composition weightpercent. For example, U.S. Pat. No. 6,077,372 to Mendenhall et al.,incorporated above, also discloses an igniter composition which iscoated onto a gas generant material including boron fuel and anoxidizer. Additionally, U.S. Pat. No. 6,132,420 to Barnes et al., whichis hereby incorporated by reference, discloses a gas-forming ignitercomposition including boron fuel, a gas-producing fuel such as guanidinenitrate, and an oxidizer. Unfortunately, boron fuels are relativelyexpensive materials and can form undesirable combustion products thatare difficult to remove from the gas stream within the inflator.Furthermore, if the boron content of an igniter composition is decreasedother mechanisms such as gas flow and heat transfer may need to beadjusted to provide the desired ballistic response.

[0009] Thus, there is a need and a demand for an igniter compositionthat provides efficient heat transfer from the gas products and fromcondensed phase products to the gas generant. In particular, there isneed and a demand for igniter compositions that generate both asignificant amount of heat and condensable products to more effectivelytransfer heat to the gas generant to promote uniform ignition of the gasgenerant. There is a further need and a demand for an ignitercomposition that is cost effective to prepare.

SUMMARY OF THE INVENTION

[0010] A general object of the invention is to provide an improvedigniter composition and method of igniting a gas generant to inflate anairbag cushion of an inflatable restraint system of a motor vehicle.

[0011] A more specific objective of the invention is to overcome one ormore of the problems described above.

[0012] The general object of the invention can be attained, at least inpart, through providing a gas-forming source of condensable copper metaleffective for transferring heat to a gas generant in an ignitercomposition containing a boron fuel component and an oxidizer, whereinthe gas-forming source of condensable copper metal is a copper complexthat includes at least one ligand selected from the group consisting ofanionic ligands, neutral alkyl ligands having at least one balancinganion, neutral ammonia ligands having at least one balancing anion, andcombinations thereof.

[0013] The prior art has generally failed to provide an ignitercomposition and a method of igniting a gas generant which is aseffective as desired in satisfying one or more of the above-identifiedperformance criteria. Further, the prior art has generally failed toprovide an igniter composition and associated method of igniting a gasgenerant related to utilizing a condensable copper metal to efficientlyand uniformly ignite a gas generant.

[0014] The invention further comprehends an igniter composition whichcontains:

[0015] about 8 to about 20 composition weight percent boron fuel;

[0016] about 30 to about 80 composition weight percent oxidizer; and

[0017] about 10 to about 40 composition weight percent gas-formingsource of condensable copper metal including a copper complex having atleast one ligand selected from anionic ligands, neutral alkyl ligandshaving at least one balancing anion, neutral ammonia ligands having atleast one balancing anion, and combinations thereof.

[0018] The invention still further comprehends a method for igniting agas generant to inflate an airbag cushion of an inflatable restraintsystem of a motor vehicle wherein an igniter composition including agas-forming copper complex is ignited such that the copper complexreacts with a boron fuel and an oxidizer to form condensable coppermetal that conducts heat to the gas generant. In accordance with oneembodiment, the method includes an igniter composition containing about10 to about 40 composition weight percent of a gas-forming coppercomplex.

[0019] References herein to a material or component as a “gas producer”or the like are to be understood to refer to high yield gas producingmaterial or components such as, when combusted with a standard oxidizersuch as sodium nitrate, produces at least about 2.5 moles of gas per 100grams of composition and preferably at least about 3.0 moles of gas per100 grams of composition.

[0020] Other objects and advantages will be apparent to those skilled inthe art from the following detailed description taken in conjunctionwith the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention provides an igniter composition such as fora gas generant material used in the inflation of inflatable devices suchas vehicle occupant restraint airbag cushions. Such combustible ignitercompositions typically include a fuel component, an oxidizer componentand a gas-form source of condensable copper metal effective fortransferring heat to the gas generant material.

[0022] It has been found that the nature of condensable products formedvia the combustion of an igniter composition plays an important role inthe ignition process. Condensable products which have a high initialtemperature, high heat content, and high thermal conductivity and whichare easily condensed upon an initially cool gas generant material aredesired to promote efficient and uniform ignition of the gas generantmaterial. Copper metal meets these criteria because it is condensed to aliquid at a high temperature and has a high thermal conductivity whichresults in more effective transfer of heat to the gas generant materialand thereby enhanced ignition of the gas generant. While it is generallyknown to include copper complexes as fuels or oxidizers in gas generantcompositions because they produce lower levels of undesirable gasproducts, lower levels of irritating or toxic particulate matter, andslag material that are easily removed from the gas stream, the use ofcopper complexes as heat conductors to promote efficient ignition of agas generant material has heretofore not been explored.

[0023] In accordance with certain preferred embodiments of theinvention, the gas-forming source of condensable copper metal used inthe practice of the invention desirably produces both a high level ofgas and an amount of copper metal condensate effective to transfer heatto a gas generant material. In particular, the gas-forming source ofcondensable copper metal can advantageously take the form of a coppercomplex including at least one ligand selected from anionic ligands,neutral alkyl ligands having at least one balancing anion, neutralammonia ligands having at least one balancing anion, and combinationthereof. Suitably, the copper complex includes a copper II cation.

[0024] Examples of anionic ligand include, but are not limited to,oxalic acid, bitetrazole, aminotetrazole, guanylurea nitrate, aceticacid, tartaric acid, 5-nitrouracil and combinations thereof. Examples ofneutral alkyl ligands include, but are not limited to,1,2-diaminopropane, 1,3-diaminopropane, and 1,3-diaminopentane. Examplesof neutral ammonia ligands include, but are not limited to, diamine andethylene diamine. Suitably, when the copper complex includes a neutralalkyl or neutral ammonia ligand at least one of the balancing anionsincludes nitrate.

[0025] In general, copper complexes such as copper oxalate, copperaminotetrazole, copper guanylurea nitrate, copper tartrate, copperbis-ethylene diamine dinitrate, and combination thereof have been foundto be particularly desirable gas-forming copper complexes for use in thepractice of the invention. The desirability of the use of thesecompounds in the igniter compositions of the invention is generallybased on a combination of factors such as relating to cost, level of gasgeneration, ease of combustion, and amount of condensable copper metalproduced.

[0026] Generally, the igniter compositions of the invention mayadvantageously contain such gas-forming copper complex in a relativeamount in the range of about 10 to about 40 composition weight percent.Practice of the invention utilizing the inclusion of such gas-formingsources of condensable copper metal within such range has been generallyfound to provide efficient heat transfer and thereby effective anduniform ignition of a gas generant material.

[0027] While various fuel materials, including boron, zirconium,titanium, magnesium, and aluminum have in the past been used in ignitercompositions in various metallic, combination or alloy forms, thepractice of the invention employing boron has been found to generallyresult or provide the most desirable level of heat production. However,the use of boron fuels result in low gas yields. Thus, it is desirableto keep the boron levels in the igniter composition as low as possible.

[0028] While the invention can be practiced utilizing such fuelcomponent in a wide range of relative amounts, in accordance withcertain preferred embodiments, such boron fuel may advantageously bepresent in the range of from about 8 to about 20 composition weightpercent, and preferably, in some embodiments, of about 8 to about 10composition weight percent. For example, operation within such ranges,particularly operation within such preferred range, can beneficiallyserve to reduce the cost of production of the ignition composition sinceboron is a relatively expensive fuel material while providing aneffective level of heat generation to promote efficient and uniformignition of a gas generant. Furthermore, use of a relatively smallamount of boron fuel reduces the production of undesirable levels ofboron combustion products which are difficult to remove from the gasstream within the inflator.

[0029] Useful igniter composition oxidizers include alkali or alkalineearth metal nitrates, particularly preferred are the nitrates of sodium,potassium, and strontium with potassium nitrate being a particularlypreferred oxidizer component for use in the practice of the invention.While the chlorates and perchlorates of alkali and alkaline earthmetals, if desired, could be used, such chlorates and perchloratesgenerally exhibit too great a sensitivity to satisfy most practicalinflatable restraint applications.

[0030] In practice, the igniter compositions of the present inventioncontain such an oxidizer component in a relative amount of between about30 to about 80 composition weight percent. One particularly preferredigniter composition contains about 60 to about 75 composition weightpercent of potassium nitrate oxidizer component.

[0031] If desired, an igniter composition in accordance with theinvention may also advantageously include an auxiliary fuel. Inparticular, the auxiliary fuel may be an organic gas-producing fuel inthe form of a nitrate of at least one amine or urea derivative. Examplesof such material include, but are not limited to, guanidine nitrate,aminoguanidine nitrate, diminoguanidine nitrate, triaminoguanidinenitrate, dicyanamide, biuret, biguanide nitrate, guanylurea nitrate,nitrotriazalone, nitrouracil, aminotetrazole, diammonium bitetrazole,bitetrazole, azodicarbonamide, cyanuric acid, alloxan, barbituric acid,nitrobarbituric acid, cyclotrimethylenetrinitramine,cyclotetramethylenetetranitramine, and combinations thereof.

[0032] In practice, the igniter compositions of the present inventionmay include an auxiliary fuel in the range of up to about 25 compositionweight percent. In one embodiment, a particularly preferred auxiliaryfuel is guanidine nitrate. The desirability of the use of guanidinenitrate in the igniter compositions of the invention is generally basedon a combination of factors such as relating to cost, stability (e.g.,thermal stability), availability and compatibility (e.g., compatibilitywith other standard or useful igniter composition ingredients, forexample).

[0033] If desired, an igniter composition in accordance with theinvention may also advantageously contain or include a relatively lowlevel or amount of a binder material. Suitable binders include, forexample, cellulose based binders such as cellulose acetate, celluloseacetate butyrate or cellulose propionate, vitons, polyvinyl pyrrolidone,polyethylene carbonate, propylene carbonate, polyvinyl chloride, andsilicone polymers and combinations thereof. While the inclusion of suchbinder material can serve various functions, in certain preferredembodiments of the invention it may be desirable to include such bindermaterial such as to facilitate subsequent processing, such as tofacilitate subsequent granulation of the igniter composition such as tofacilitate the formation of comparatively larger sized granules. Inpractice, the inclusion of such binder material in an amount of no morethan about 5 composition weight percent has been found to be generallyeffective for such uses.

[0034] Additional additives such as flow aids, burn rate catalysts,viscosity modifiers, pressing aids, dispersing aids, or phlegmatizingagents may also be included in the igniter composition to facilitateprocessing or to provide enhanced properties. Generally, such additivesmay be included in the igniter composition in an amount of no more thanabout 5 composition weight percent.

[0035] The igniter compositions of the invention are advantageously andpreferably ignitable by means of standard squib devices. Such squibdevices typically include a bridgewire, an initiating explosive and apyrotechnic output charge such as zirconium potassium perchlorate(commonly referred to as “ZPP”), for example. In practice, suchpyrotechnic means of initiation commonly produce or form reactionproducts which in turn contact or otherwise initiate reaction of theigniter composition used in association therewith.

[0036] As will be appreciated, the compatibility of the subject ignitercompositions with such standard squib devices facilitates theincorporation and use of such igniter compositions in various inflatoror airbag systems without requiring special or possible costly design orprocessing modifications. As a result, various of the beneficial aspectsof the igniter compositions of the invention and the uses thereof forgas generation such as relating to effective heat transfer from thecombustion products of the igniter composition to a gas generantmaterial to efficiently and uniformly ignite a gas generant, can morereadily and practically be realized.

[0037] The present invention is described in further detail inconnection with the following examples which illustrate or simulatevarious aspects involved in the practice of the invention. It is to beunderstood that all changes that come within the spirit of the inventionare desired to be protected and thus the invention is not to beconstrued as limited by these examples.

EXAMPLES

[0038] TABLE 1, below, provides the compositional make-up of fivespecific igniter compositions in accordance with the present invention.The igniter compositions were prepared by slurry mixing the solid rawingredients with a 50/50 mixture of water and ethyl alcohol. Themixtures were then dried in an air stream until the liquid concentrationwas about 10 percent by weight. At this point the mixtures weregranulated to a 14 mesh size and dried to completeness in a vacuum oven.The dried mixtures were again granulated to a 14 mesh size to yield thefinal igniter compositions. TABLE 1 Composition Ingredient (wt %) 1 2 34 5 Boron  9.00  9.00  9.47  9.00 8.0 Guanidine nitrate 15.35 12.34 9.33 — — Potassium nitrate 60.05 68.89 67.50 73.49 62.90 Copper oxalate15.00 — — — — Copper aminotetrazole — 10.23 — — — Copper tartrate — —14.13 — — Copper bis-ethylene diamine dinitrate — — — 17.50 — Copperguanylurea nitrate — — — — 29.10

Example 1

[0039] Two grams of each of the Compositions in TABLE 1 was burned underlaboratory conditions and the rate of burning of each composition wasvisually compared with that of a standard boron/potassium nitrateigniter composition including about 25 composition weight percent boronand about 75 composition weight percent potassium nitrate. The rate ineach case was visually observed to be greater than or equal to that ofthe standard composition. All of the compositions of TABLE 1 exhibitedsigns of having produced condensable copper metal in the form of coppervapor since copper metal deposits were observed around the cooled burnarea.

Example 2

[0040] Compositions 1 and 2 of TABLE 1 were further subjected toballistic testing by firing two grams of each composition into astandard vented bomb and using two grams of each composition to ignite34 grams of a standard gas generant in an inflator device (inflatortest). In each test, the performance of both compositions exceeded theperformance of the standard boron/potassium nitrate igniter compositiondescribed above. In the vented bomb test, the peak pressures obtainedfor compositions 1 and 2 were higher (at shorter time) as compared tothe standard igniter composition. In the inflator test, higher peakpressures were measured for compositions 1 and 2 at shorter times ascompared to the standard igniter composition.

[0041] The invention illustratively disclosed herein suitably may bepracticed in the absence of any element, part, step, component, oringredient which is not specifically disclosed herein.

[0042] While in the foregoing detailed description this invention hasbeen described in relation to certain preferred embodiments thereof, andmany details have been set forth for purposes of illustration, it willbe apparent to those skilled in the art that the invention issusceptible to additional embodiments and that certain of the detailsdescribed herein can be varied considerably without departing from thebasic principles of the invention.

What is claimed is:
 1. An igniter composition comprising: boron fuel: an oxidizer: and a gas-forming source of condensable copper metal effective for transferring heat to a gas generant, wherein the gas-forming source of condensable copper metal is a copper complex that includes at least one ligand selected from the group consisting of anionic ligands, neutral alkyl ligands having at least one balancing anion, neutral ammonia ligands having at least one balancing anion, and combinations thereof.
 2. The igniter composition of claim 1 wherein the copper complex comprises a copper II cation.
 3. The igniter composition of claim 1 wherein the copper complex comprises at least one anionic ligand selected from the group consisting of oxalic acid, bitetrazole, aminotetrazole, guanylurea nitrate, acetic acid, tartaric acid, 5-nitrouracil, and combinations thereof.
 4. The igniter composition of claim 1 wherein the copper complex comprises at least one neutral alkyl ligand selected from the group consisting of 1,2-diaminopropane, 1,3-diaminopropane, and 1,3-diaminopentane.
 5. The igniter composition of claim 4 wherein at least one balancing anion comprises nitrate.
 6. The igniter composition of claim 1 wherein the copper complex comprises at least one neutral ligand selected from the group consisting of diamine and ethylene diamine.
 7. The igniter composition of claim 6 wherein at least one balancing anion comprises nitrate.
 8. The igniter composition of claim 1 further comprising an auxiliary fuel.
 9. The igniter composition of claim 1, further comprising a binder composition.
 10. An igniter composition comprising: about 8 to about 20 composition weight percent boron; about 30 to about 80 composition weight percent oxidizer; and about 10 to about 40 composition weight percent gas-forming source of condensable copper metal effective for transferring heat to a gas generant, wherein the gas-forming source of condensable copper metal includes a copper complex having at least one ligand selected from the group consisting anionic ligands, neutral alkyl ligands having at least one balancing anion, neutral ammonia ligands having at least one balancing anion, and combinations thereof.
 11. The igniter composition of claim 10 wherein the copper complex comprises a copper II cation.
 12. The igniter composition of claim 10 wherein the copper complex comprises at least one anionic ligand selected from the group consisting of oxalic acid, bitetrazole, aminotetrazole, guanylurea nitrate, acetic acid, tartaric acid, 5-nitrouracil, and combinations thereof.
 13. The igniter composition of claim 12 wherein the copper complex comprises copper oxalate, copper aminotetrazole, copper guanylurea nitrate, or copper tartrate.
 14. The igniter composition of claim 10 wherein the copper complex includes at least one neutral alkyl ligand selected from the group consisting of 1,2-diaminopropane, 1,3-diaminopropane, and 1,3-diaminopentane.
 15. The igniter composition of claim 14 wherein at least one balancing anion comprises nitrate.
 16. The igniter composition of claim 10 wherein the copper complex includes at least one neutral ammonia ligand selected from the group consisting of diamine and ethylene diamine.
 17. The igniter composition of claim 16 wherein at least one balancing anion is nitrate.
 18. The igniter composition of claim 17 wherein the copper complex comprises copper bis-ethylenediamine dinitrate.
 19. The igniter composition of claim 10 wherein the oxidizer comprises potassium nitrate.
 20. The igniter composition of claim 10 further comprising up to about 25 composition weight percent auxiliary fuel.
 21. The igniter composition of claim 20 wherein the auxiliary fuel comprises guanidine nitrate.
 22. The igniter composition of claim 10 further comprising up to about 5 composition weight percent binder.
 23. A method for igniting a gas generant to inflate an airbag cushion of an inflatable restraint system of a motor vehicle comprising the steps of: providing an igniter composition including boron fuel, an oxidizer and a gas-forming copper complex including at least one ligand selected from the group consisting of anionic ligands, neutral alkyl ligands having at least one balancing anion, neutral ammonia ligands having at least one balancing anion, and combinations thereof; and igniting the igniter composition such that the gas-forming copper complex reacts with the boron fuel and the oxidizer to form a gas and condensable copper metal that conducts heat to the gas generant.
 24. The method of claim 23 wherein the igniter composition comprises: about 8 to about 20 composition weight percent boron fuel; about 30 to about 80 composition weight percent oxidizer; and about 10 to about 40 composition weight percent gas-forming copper complex.
 25. The method of claim 24 wherein the gas-forming copper complex is selected from the group consisting of copper oxalate, copper aminotetrazole, copper guanylurea nitrate, copper tartrate, copper bis-ethylenediamine dinitrate, and combinations thereof.
 26. The method of claim 24 wherein the oxidizer is potassium nitrate.
 27. The method of claim 24 wherein the igniter composition further comprises up to about 25 composition weight percent auxiliary fuel.
 28. The method of claim 27 wherein the auxiliary fuel comprises guanidine nitrate.
 29. The method of claim 24 further comprising the step of providing a pyrotechnic squib.
 30. The method of claim 29 further comprising the step of contacting the igniter composition with reaction products from the pyrotechnic squib to ignite the igniter composition. 